The most common and most likely answer to this crossword clue is the 7 letter word HADRIAN
I've seen this crossword clue in Financial Times
H
A
D
R
I
A
N
More clues leading to the result HADRIAN
- Emperor beginning to hate English pope
- Old ruler had managed to seize India's capital
- Emperor had managed to capture island
- Waller took top tip from Roach – piano’s inside
- 18 Emperor, experienced, managed to keep grip on Italy
- Area drain faulty
- Emperor possessed by new manner after revolution
- He built a wall and kept rain out
- Pope
- Emperor, possessed, managed to capture island
Buddy explains!
The straight part
We know that "Waller" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case waller = hadrian.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.